A photodetector IC (PDIC) includes an array of discrete photodiodes (a photodiode array or “PDA”) on a common substrate material, typically a silicon chip, amplifiers, and readout circuitry. Electromagnetic radiation received by the photodiodes generates electron-hole pairs, and the electrons migrate to the nearest junction, typically a PIN junction or a NIP junction. A PIN or NIP junction is a diode with a wide, lightly doped near-intrinsic semiconductor region (I) between a p-type semiconductor and an n-type semiconductor region which are both typically heavily doped as they are used for ohmic contacts. The light doping level in the intrinsic region results in low junction capacitance for both junctions. After a fixed integration time the charge accumulated at each PD element is sequentially read with readout circuitry to generate the electrical response of the PDIC.
Some PDICs are used for processing CD, DVD and Blu-ray formats as part of an optical pick-up apparatus, where CD, DVD and Blu-ray each operate at different wavelengths (bands). A typical optical pick-up apparatus enables information to be recorded, reproduced and erased with respect to a CD group disc (e.g. CD, CD-ROM, CD-R and CD-RW), a DVD group disc (e.g. DVD, DVD-ROM, DVD-RAM, DVD-R and DVD-RW, DVD+R, DVD+RW), and Blu-ray format discs, with single or multiple layer formats. The typical optical pick-up apparatus has an infrared semiconductor laser device for the CD (at about 780 nm), a red semiconductor laser device for the DVD (at about 650 nm) and a blue laser device for the Blu-ray (at about 405 nm). During operation of the optical pick-up apparatus a portion of the light from the respective lasers and a portion of the light from the respective group discs is directed by a beam splitter to the PDs of the PDA.
Generally, the process used to form PDAs forms a single Anti-Reflective Coating (ARC) having a particular ARC film structure (materials and/or thicknesses) designed so that one of the bands (CD, DVD or Blu-ray) is processed at a high sensitivity. Sensitivity for a photodiode is generally defined as the ratio of its output current to incident light power (e.g., in amps/watt (A/W)). For example, the ARC stack for the photodiodes may be designed so that the Blu-ray band (405 nm radiation) may have nearly its highest possible sensitivity.